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| Book/Report | FZJ-2019-00381 |
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1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21208
Report No.: Juel-3022
Abstract: With a newly developed KKR Green's function method for defects at surfaces in local spin density approximation we present calculations for the electronic structureof 3d, 4d and 5d transition-metal impurities and 4d and 5d transition-metal clusters at the (001) surfaces of Cu and Ag . We focused especially on the magnetism of the investigated structures. In the first part of this work we discuss a generalization of Green's functions by using the Fermi-Dirac distribution for finite temperatures together with the method of complex energy integration. It is shown that the energy functional has to be generalized to a grandcanonical functional to guarantee its extremal properties. Test calculations for different temperatures are presented to clarify the influence of temperature on ground state properties.Next we present density functional calculations for the magnetic moments of 3d, 4d and 5d impurities in and on Cu and Ag (001) surfaces, systems which have notbeen studied by ab-initio methods before. The local magnetic moments of 3d impurities at the Cu surface are strongly enhanced, which is especially pronounced forCr and V. While 4d and 5d impurities are in general non-magnetic in the bulk, our calculations yield large magnetic moments for 4d (Nb, Mo, Tc, Ru) and 5d (Ta, W, Re) impurity atoms at the Ag (001) surface. Some of the adatoms (Nb, Mo, Tc, W, Re) on Ag (001) have "giant" magnetic moments between 3 And 4 $\mu_{B}$. The stability of the moments is analysed in terms of the spin-polarization energies. Our results for single adatoms are compared in detail with calculations for the corresponding monolayers. In the last chapter we present ab-initio calculations for the electronic structure of 4d and 5d transition-metal clusters at the (001) surface of Ag by concentrating on the formation of magnetic moments. A variety of geometrical structures, like dinners, linear chains and plane islands is investigated, all showing a strong tendency for magnetism. Due to the hybridisation with the substrate and with the adatoms within the clusters the maximum of the local moments is shifted to higher valencies. Compared with single adsorbate atoms the magnetism of the clusters sensitively depends on their size and geometry.
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